Russia's President Vladimir Putin has warned his country's enemies they will "be served with poison".

Mr Putin made his comments at a time when British police are investigating the apparent poisoning of a Russian double agent and his daughter in Salisbury, England, although he was not addressing that issue when he made the comments.

He said Western sanctions for Moscow's annexation of Crimea and the insurgency in eastern Ukraine were part of "illegitimate and unfair" efforts to contain Russia, but added that "we will win in the long run". He continued: "Those who serve us with poison will eventually swallow it and poison themselves."

Speaking in an interview with the Russian state television, Mr Putin lavished US President Donald Trump with praise, describing him as a great communicator.

"I have no disappointment at all," Mr Putin said when asked about the US president. "Moreover, on a personal level he made a very good impression on me."

The two leaders met on the sidelines of international summits last year.

Mr Putin praised Mr Trump as a "balanced" man, who easily gets into the gist of various issues and listens to his interlocutor. "It's possible to negotiate with him, to search for compromises," Mr Putin added.

He also noted that he spent some time talking to Melania Trump when he sat next to her during an official dinner at the G20 summit in Hamburg, Germany, in July.

The Russian leader said he told her and the wife of the Italian premier "about Siberia and Kamchatka, about fishing ... about bears on Kamchatka and tigers in the Far East".

"I made some exaggerations," the action-loving Russian leader said with a grin. "When you talk about fishing, you can't help exaggerating."

Asked if he was trying to recruit the women, the KGB veteran responded by saying: "No, I stopped dealing with that a long time ago."

He added with a smile: "But I liked doing that, it was my job for many years."

Venting his frustration with the US political system, Mr Putin said: "It has demonstrated its inefficiency and has been eating itself up."

"It's quite difficult to interact with such a system, because it's unpredictable," Mr Putin said.

Moscow's hopes for better ties with Washington have been dashed by the ongoing congressional and FBI investigations into allegations of collusion between Mr Trump's campaign and Russia.

Speaking about the bitter tensions in Russia-West relations, Mr Putin said they have been rooted in Western efforts to contain and weaken Russia.

"We are a great power, and no one likes competition," he said.

He said he was particularly dismayed by what he ­described as the US role in the ousting of Ukraine's Russia-friendly president in February 2014 amid massive protests.

Responding to a question about Russia's growing global leverage, Mr Putin responded: "If we play strongly with weak cards, it means the others are just poor players, they aren't as strong as it seemed, they must be lacking something."

Mr Putin, who presented a sweeping array of new Russian nuclear weapons last week, voiced hope that nuclear weapons will never be used but warned that Russia will retaliate in kind if it comes under a nuclear attack.

"The decision to use nuclear weapons can only be made if our early warning system not only detects a missile launch but clearly forecasts its flight path and the time when warheads reach the Russian territory," he said. "If someone makes a decision to destroy Russia, then we have a legitimate right to respond." He added starkly: "Yes, it will mean a global catastrophe for mankind, for the entire world. But as a citizen of Russia and the head of Russian state I would ask: What is such a world for, if there were no Russia?"

British Prime Minister Theresa May has backed moves to snub the World Cup in Russia - if Kremlin links are proven in the Salisbury contamination scare. Mrs May told MPs that her government would "look at whether ministers and other dignitaries should attend" the tournament after a former Russian double agent Sergei Skripal (66), and his 33-year-old daughter Yulia were taken to hospital with "suspected exposure to an unknown substance".

Mr Skripal was convicted in 2006 of passing state secrets to MI6 before being given refuge in the UK as part of a spy swap.